1. Field of the Invention
The present invention relates to an image heating apparatus for heating an image borne by a recording material by passing the recording material through a fixing nip portion N between a heat member and a pressuring member to cause the material to be held and conveyed. Particularly, the present invention relates to an image heating apparatus to be preferably mounted on an image forming apparatus such as a copying machine or printer as an image heating-fixing device.
More minutely, the present invention includes a flexible sleeve-shaped rotor, a sliding member set to the inside of the rotor to slide on the inner periphery of the rotor, a pressuring member for forming a nip portion together with the sliding member by holding the rotor and a regulation member set by facing the end of the rotor to regulate movement of the rotor in a generatrix direction, which heats a recording material bearing an image by the nip portion while conveying the recording material.
2. Related Background Art
The heating roller system shown in FIG. 15 has been used so far as an image heating apparatus to be mounted on a copying machine or printer as a fixing device. This system is basically constituted of a metallic heating roller 202 including a halogen heater 201 and an elastic pressuring roller 203 pressure-welded to the heating roller 202. Moreover, a recording medium S bearing an unfixed toner image t as a member to be heated is introduced into the fixing nip portion N (fixing nip portion) of the roller pair 202 and 203 to hold, convey and pass the recording medium S. Thereby, the toner image t is heated, pressured and fixed.
However, the fixing device according to the heating roller system requires a lot of time in order to raise the temperature of roller surface up to a fixing temperature because the rollers respectively have a large heat capacity. Therefore, to quickly execute the image output operation, it is necessary to keep the roller surface at a certain degree of temperature also when the apparatus is not used.
Therefore, a film-heating-system heating apparatus for fixing a developer to a recording medium by using a film heated by a heater is proposed as an on-demand type heating apparatus.
This film-heating-system heating apparatus normally has a thin heat-resistant film (e.g. polyimide) and a heater (heat generation member) fixed to one side of the film. Moreover, the apparatus has a pressure roller set to the other side of the film by facing a heater to contact a member to be heated with the heater through the film.
Moreover, when using the pressure roller as a fixing device, a recording medium making the fixing nip portion N (fixing nip portion) formed by pressure welding between the heater and pressure roller at both sides of the film form and bear a toner image is introduced and passed. Thereby, the visualized image bearing body face of the recording medium is heated by the heater through the film, heat energy is supplied to an unfixed image, toner is softened and melted and the image is heated and fixed.
In the case of the above film-heating-system heating apparatus, it is possible to use a low-heat-capacity heater as a heat generation member. Therefore, it is possible to save power and shorten the wait time compared to the case of a conventional heat-roller-system or belt-heating-system apparatus.
Moreover, it is recently proposed to prevent luster irregularity of an image by setting an elastic layer to the outside of a fixing film and uniforming the contact between a recording material having minute irregularity and the film. Furthermore, an apparatus is proposed which secures the on-demand property of a fixing device by using a metallic film having a heat conductivity higher than that of the polyimide film (e.g. stainless steel) in order to prevent deterioration of heat conductivity caused as a harmful result of setting the elastic layer.
In the case of these film-heating-system fixing devicees, lateral shift to the generatrix direction (thrust direction) may occur in a film and it is difficult to regulate the lateral shift force. Particularly, when a displacement of the parallelism between a pressure roller and the film or the right-left difference of applied pressure increases, a strong hook-approach force is generated and a strong stress is applied to the end of the film. Therefore, the end of the film may be damaged.
Therefore, it is proposed to regulate lateral shift by loosely winding a film, decreasing the lateral shift force of the film, and receiving the film end by the film-edge part regulation surface (hereafter also referred to as “regulation face”) of a flange in Japanese Patent Application Laid-Open No. H04-044075 and Japanese Patent Application Laid-Open No. H04-204980. When a fixing film is flexible enough and loose pulling is possible, it is possible to avoid film damage by the configuration disclosed in the above documents. However, in the case of a fixing belt using a metallic film, the fixing film itself has a high stiffness and lacks in flexibility. Therefore, when the shift of parallelism between the above pressure rollers and film or the difference between right and left applied pressures arises and a strong lateral shift force is generated and a film locally receives a stress on the lateral shift regulation surface, cracks may arise from an end.